a. Field of the Invention
The instant invention relates to modeling of tissue surfaces. In particular, the instant invention relates to a system and method for distinguishing surface points from interior points during the collection of geometry points.
b. Background Art
It is well known to generate heart chamber geometry in preparation for cardiac diagnostic or therapeutic procedures. Often, a catheter tip is placed against the wall of the heart chamber and the three-dimensional coordinates of the catheter tip measured using a localization system. The three-dimensional coordinates become a geometry point. Multiple measurements are taken as the catheter is moved within the heart chamber, resulting in a cloud of geometry points (also referred to as “location data points”) that defines the geometry of the heart chamber. Various surface construction algorithms may then be applied to wrap a surface around the cloud of geometry points to obtain a representation of the heart chamber geometry.
While gathering geometry points, it is desirable that the catheter only visit sites within the heart chamber of interest. In practice, however, the catheter will, from time to time, slip into another chamber or structure. For example, in a right atrial study, it is not uncommon for the catheter to slip through the tricuspid valve into the right ventricle. The result of this detour is the acquisition of a large number of erroneous geometry points that must be deleted by the operator in order to input a valid set of geometry points to the surface construction algorithm.
In addition, due to cardiac motion (e.g., the beating of the heart), the catheter may experience oscillations. Depending on how oscillations are accounted for (e.g., by averaging catheter position over one or more heart cycles), it is possible to acquire erroneous geometry points lying outside the true geometry of the beating heart that must be manually deleted to provide a valid set of geometry points to the surface construction algorithm. For example, it the catheter suddenly changes from one generally stable position on the surface of the heart to another generally stable position on the surface of the heart, an averaging or filtering process may create a more or less straight route between the two positions, part of which may lie inside or outside the true boundaries of the heart chamber, while the actual route taken was a curve coincident with the boundaries of the heart chamber.
Further, in order to reduce overhead and time required to perform the surface construction algorithm, it is desirable that the cloud of geometry points include points on the surface of the heart chamber (“surface points”) and exclude points not on the surface of the heart chamber (“interior points”). Unfortunately, just as it is not uncommon for the catheter to inadvertently move into an adjoining structure, it is similarly not uncommon for the catheter to occasionally break contact with the surface and fall into the interior of the heart chamber, resulting in the collection of interior points in addition to surface points.